A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSiSiR (R = Si^<i>i</i>Pr[CH(SiMe₃)₂]) with Isocyanides

The reaction of 1,1,4,4-tetrakis­[bis­(trimethylsilyl)­methyl]-1,4-diisopropyltetrasila-2-yne (<b>1</b>) with <i>tert</i>-butylisocyanide or <i>tert</i>-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR­(CNR′)₂] (R = Si^<i>i</i>Pr­[CH­(SiMe₃)₂]₂, R′ = ^<i>t</i>Bu (<b>2a</b>) or CMe₂CH₂^<i>t</i>Bu (<b>2b</b>)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of <b>2a</b>, X-ray crystallography. Upon warming to room temperature, <b>2</b> underwent thermal decomposition to produce 1,2-dicyanodisilene R­(NC)­SiSi­(CN)­R (<b>3</b>) and 1,2-dicyanodisilane R­(NC)­HSiSiH­(CN)­R (<b>4</b>) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative <b>3</b> was characterized by X-ray crystallography

A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSiSiR (R = Si^<i>i</i>Pr[CH(SiMe₃)₂]) with Isocyanides

The reaction of 1,1,4,4-tetrakis­[bis­(trimethylsilyl)­methyl]-1,4-diisopropyltetrasila-2-yne (<b>1</b>) with <i>tert</i>-butylisocyanide or <i>tert</i>-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR­(CNR′)₂] (R = Si^<i>i</i>Pr­[CH­(SiMe₃)₂]₂, R′ = ^<i>t</i>Bu (<b>2a</b>) or CMe₂CH₂^<i>t</i>Bu (<b>2b</b>)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of <b>2a</b>, X-ray crystallography. Upon warming to room temperature, <b>2</b> underwent thermal decomposition to produce 1,2-dicyanodisilene R­(NC)­SiSi­(CN)­R (<b>3</b>) and 1,2-dicyanodisilane R­(NC)­HSiSiH­(CN)­R (<b>4</b>) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative <b>3</b> was characterized by X-ray crystallography

A New Disilene with π-Accepting Groups from the Reaction of Disilyne RSiSiR (R = Si^<i>i</i>Pr[CH(SiMe₃)₂]) with Isocyanides

The reaction of 1,1,4,4-tetrakis­[bis­(trimethylsilyl)­methyl]-1,4-diisopropyltetrasila-2-yne (<b>1</b>) with <i>tert</i>-butylisocyanide or <i>tert</i>-octylisocyanide produced the corresponding disilyne–isocyanide adducts [RSiSiR­(CNR′)₂] (R = Si^<i>i</i>Pr­[CH­(SiMe₃)₂]₂, R′ = ^<i>t</i>Bu (<b>2a</b>) or CMe₂CH₂^<i>t</i>Bu (<b>2b</b>)), which are stable below −30 °C and were characterized by spectroscopic data and, in the case of <b>2a</b>, X-ray crystallography. Upon warming to room temperature, <b>2</b> underwent thermal decomposition to produce 1,2-dicyanodisilene R­(NC)­SiSi­(CN)­R (<b>3</b>) and 1,2-dicyanodisilane R­(NC)­HSiSiH­(CN)­R (<b>4</b>) via C–N bond cleavage and elimination of an alkane and an alkene. The 1,2-dicyanodisilene derivative <b>3</b> was characterized by X-ray crystallography

Frustrated Lewis Pair Route to Hydrodesilylation of Silylphosphines

A 1:1 mixture of P­(SiMe₃)₃ and B­(<i>p</i>-C₆F₄H)₃ reacts with 3 equiv of 4-heptanone to afford a 1:2 mixture of [(Me₃SiO)­(<i>n</i>-Pr)₂C]­H₂P–B­(<i>p</i>-C₆F₄H)₃ and the silyl enol ether, 4-trimethylsiloxy-3-heptene. Subsequent thermolysis of the adduct produces H₃P–B­(<i>p</i>-C₆F₄H)₃ and an additional equiv of silyl enol ether. In the presence of a catalytic quantity of B­(<i>p</i>-C₆F₄H)₃, however, P­(SiMe₃)₃ reacts with 4-heptanone to produce a 1:1 mixture of [(Me₃SiO)­(<i>n</i>-Pr)₂C]₂PH and silyl enol ether. Heating this mixture further produces [(Me₃SiO)­(<i>n</i>-Pr)₂C]­PH₂, which is eventually converted to elemental phosphorus

Frustrated Lewis Pair Route to Hydrodesilylation of Silylphosphines

A 1:1 mixture of P­(SiMe₃)₃ and B­(<i>p</i>-C₆F₄H)₃ reacts with 3 equiv of 4-heptanone to afford a 1:2 mixture of [(Me₃SiO)­(<i>n</i>-Pr)₂C]­H₂P–B­(<i>p</i>-C₆F₄H)₃ and the silyl enol ether, 4-trimethylsiloxy-3-heptene. Subsequent thermolysis of the adduct produces H₃P–B­(<i>p</i>-C₆F₄H)₃ and an additional equiv of silyl enol ether. In the presence of a catalytic quantity of B­(<i>p</i>-C₆F₄H)₃, however, P­(SiMe₃)₃ reacts with 4-heptanone to produce a 1:1 mixture of [(Me₃SiO)­(<i>n</i>-Pr)₂C]₂PH and silyl enol ether. Heating this mixture further produces [(Me₃SiO)­(<i>n</i>-Pr)₂C]­PH₂, which is eventually converted to elemental phosphorus

Synthesis and Structures of Nickel Complexes with a PN-Chelate Phosphaalkene Ligand

Phosphaalkenes with a PC bond possess extremely strong π-accepting ability, often providing transition metal complexes with interesting structures and properties. This paper describes unique structures of nickel complexes coordinated with a PN-chelate phosphaalkene ligand (PEP = 2-[1-phenyl-2-(2,4,6-tri-<i>tert</i>-butylphenyl)-2-phosphaethenyl]­pyridine). The PEP ligand combines with [NiBr₂(dme)] (dme = 1,2-dimethoxyethane) in toluene to afford [Ni­(Br)­(μ-Br)­(PEP)]₂ (<b>1</b>), which reacts with R₂Mg­(thf)₂ in Et₂O or THF to form three types of nickel complexes depending on the R groups and reaction conditions. The reaction with Ph₂Mg­(thf)₂ produces a Ni­(I) dimer bridged with two μ-Br ligands, [Ni­(μ-Br)­(PEP)]₂ (<b>2</b>). Treatment of <b>1</b> with R₂Mg­(thf)₂ (R = Me, Me₃SiCH₂) at −35 °C leads to dialkyl complexes [NiR₂(PEP)] (<b>3</b> and <b>4</b>), with a significantly distorted square planar configuration. DFT calculations support the occurrence of effective π-back-bonding between Ni to PEP to cause the structural distortion. On the other hand, the reaction of <b>1</b> with R₂Mg­(thf)₂ (R = Me₃SiCH₂) conducted at a low temperature of −78 °C forms an aryl bromide complex of the formula [Ni­(Mes*)­(Br)­(PEP*)] (<b>5</b>; Mes* = 2,4,6-^<i>t</i>Bu₃C₆H₂), in which the Mes* group originally bonded to the phosphorus atom of PEP is shifted to nickel; instead, the phosphorus atom is substituted with the R group to form the PEP* ligand. The temperature-dependent formation of <b>4</b> or <b>5</b> is rationalized by considering a common five-coordinate intermediate

C–H Bond Cleavage of Acetonitrile by Iridium Complexes Bearing PNP-Pincer-Type Phosphaalkene Ligands

A novel parent amido complex of iridium­(I), K­[Ir­(NH₂)­(PPEP*)] (<b>3</b>), coordinated with a dearomatized PNP-pincer-type phosphaalkene ligand (PPEP*) has been prepared by deprotonation with KHMDS from [Ir­(NH₂)­(PPEP)] (<b>2</b>) having benzophospholanylmethyl and phosphaethenyl groups at the 2,6-positions of pyridine. Complex <b>3</b> has two base points at PPEP* and NH₂ ligands and, thus, successively reacts with two molecules of CH₃CN via heterolytic cleavage of the C–H bond. X-ray structural analysis of the product complex K­[Ir­(CH₂CN)₂(PPEP)] (<b>5</b>) reveals remarkable elongation of the PC bond indicative of the occurrence of strong π-back-donation from iridium to PPEP

C–H Bond Cleavage of Acetonitrile by Iridium Complexes Bearing PNP-Pincer-Type Phosphaalkene Ligands

A novel parent amido complex of iridium­(I), K­[Ir­(NH₂)­(PPEP*)] (<b>3</b>), coordinated with a dearomatized PNP-pincer-type phosphaalkene ligand (PPEP*) has been prepared by deprotonation with KHMDS from [Ir­(NH₂)­(PPEP)] (<b>2</b>) having benzophospholanylmethyl and phosphaethenyl groups at the 2,6-positions of pyridine. Complex <b>3</b> has two base points at PPEP* and NH₂ ligands and, thus, successively reacts with two molecules of CH₃CN via heterolytic cleavage of the C–H bond. X-ray structural analysis of the product complex K­[Ir­(CH₂CN)₂(PPEP)] (<b>5</b>) reveals remarkable elongation of the PC bond indicative of the occurrence of strong π-back-donation from iridium to PPEP

Catalytic Synthesis of an Unsymmetrical PNP-Pincer-Type Phosphaalkene Ligand

An unsymmetrical PNP-pincer-type phosphaalkene ligand, 2-(phospholanylmethyl)-6-(2-phosphaethenyl)­pyridine (PPEP), has been prepared from 2,6-bis­(2-phosphaethenyl)­pyridine (BPEP) by intramolecular C–H addition/cyclization of the 2-phosphaethenyl group with a 2,4,6-tri<i>-tert</i>-butylphenyl substituent (CHPMes*). The reaction proceeds in hexane in the presence of a catalytic amount of [Pt­(PCy₃)₂] (20 mol %) at 80 °C in a sealed tube, giving PPEP in 32% isolated yield, along with byproduction of 2,6-bis­(phospholanylmethyl)­pyridine (BPMP) and a Pt­(II) phosphanido complex (<b>5</b>). The PPEP ligand reacts with [Rh­(μ-Cl)­(C₂H₄)₂]₂ and [RuCl₂(PPh₃)₃] to afford [RhCl­(PPEP)] (<b>6</b>) and [RuCl₂(PPh₃)­(PPEP)] (<b>8</b>), respectively. Complex <b>6</b> easily undergoes C–H addition/cyclization at the other CHPMes* group to afford the 2,6-bis­(phospholanylmethyl)­pyridine complex [RhCl­(BPMP)] (<b>7</b>), whereas <b>8</b> is stable against C–H addition/cyclization. Treatment of <b>8</b> with ^<i>t</i>BuOK forms [RuCl­(PPh₃)­(PPEP*)] (<b>9</b>), coordinated with an unsymmetrical PNP-pincer-type phosphaalkene ligand containing a dearomatized pyridine unit (PPEP*). The X-ray structures of <b>5</b> and <b>9</b> are reported. The reaction processes from BPEP to PPEP and to <b>5</b> are discussed based on NMR observations

Catalytic Synthesis of an Unsymmetrical PNP-Pincer-Type Phosphaalkene Ligand

An unsymmetrical PNP-pincer-type phosphaalkene ligand, 2-(phospholanylmethyl)-6-(2-phosphaethenyl)­pyridine (PPEP), has been prepared from 2,6-bis­(2-phosphaethenyl)­pyridine (BPEP) by intramolecular C–H addition/cyclization of the 2-phosphaethenyl group with a 2,4,6-tri<i>-tert</i>-butylphenyl substituent (CHPMes*). The reaction proceeds in hexane in the presence of a catalytic amount of [Pt­(PCy₃)₂] (20 mol %) at 80 °C in a sealed tube, giving PPEP in 32% isolated yield, along with byproduction of 2,6-bis­(phospholanylmethyl)­pyridine (BPMP) and a Pt­(II) phosphanido complex (<b>5</b>). The PPEP ligand reacts with [Rh­(μ-Cl)­(C₂H₄)₂]₂ and [RuCl₂(PPh₃)₃] to afford [RhCl­(PPEP)] (<b>6</b>) and [RuCl₂(PPh₃)­(PPEP)] (<b>8</b>), respectively. Complex <b>6</b> easily undergoes C–H addition/cyclization at the other CHPMes* group to afford the 2,6-bis­(phospholanylmethyl)­pyridine complex [RhCl­(BPMP)] (<b>7</b>), whereas <b>8</b> is stable against C–H addition/cyclization. Treatment of <b>8</b> with ^<i>t</i>BuOK forms [RuCl­(PPh₃)­(PPEP*)] (<b>9</b>), coordinated with an unsymmetrical PNP-pincer-type phosphaalkene ligand containing a dearomatized pyridine unit (PPEP*). The X-ray structures of <b>5</b> and <b>9</b> are reported. The reaction processes from BPEP to PPEP and to <b>5</b> are discussed based on NMR observations